There are at least five genetically distinct collagen types whose degradation may be controlled independently. The initial step of collagen degradation is performed by collagenase. We and others have found that type IV basement membrane collagen is not degraded by human skin collagenase suggesting that a separate collagenase may degrade type IV collagen. A collagenase which preferentially degrades type IV collagen has been derived from a metastasis of the T241 fibrosarcoma. This collagenase has been purified 1000-fold and its cleavage products have been partially characterized. We are further studying the secretion rate of this enzyme by a wide variety of cell types both normal and malignant.